The present invention relates to a process for preparing mono, di and polythio-bisphenol phosphorus acid esters. Particularly, the present invention relates to a process for preparing sulfur linked aryl esters of pentavalent phosphorus acids.
More particularly, the present invention relates to a process for preparing compounds which are used as insecticides, lubricant additives, functional fluids, fuel additives, plasticizers and stabilizers for plastics such as PVC, polyethylene and polypropylene, and thermoplastic and thermoset polymers.
Many types of materials compete to meet the high performance characteristics needed in modern functional fluids. Materials used in this field are petroleum mineral oils, synthetic ester fluids, polyether fluids, silicone fluids, chlorinated biphenyls, and esters and amides of phosphorus.
However, difficulties exist in the application of available materials to functional fluid use because of the extreme operating conditions encountered in modern machinery. To be effective, functional fluids used as lubricants under extreme conditions must be viscous materials.
The need for high viscosity fluids requires the incorporation of polymeric viscosity improvers into the fluids which can give rise to problems of sludging and changes of viscosity under the rigors of time and high shear. Heavy duty applications require the use of load bearing additives to increase the load bearing abilities of the fluids. In addition, the fluids are subject to oxidative breakdown requiring the use of oxidation and corrosion inhibitors in formulations. The wide variety of additives has led to increased formulation difficulties in most functional fluid systems.
Of all the presently commercially available functional fluids, the phosphate esters have become the most attractive because of their relatively low cost, flame resistance, moderately low vapor pressure and useful range of viscosity. However, functional fluids based on phosphorus esters have encountered increased formulation difficulties in attempting to extend their properties to meet extreme operating conditions.
It has now been found that new classes of compounds can be provided by a simple and direct synthesis method from readily available starting materials, which compounds generally have good lubricity and load bearing properties, oxidation and corrosion inhibiting properties and excellent compatibility with petroleum and synthetic lubricating oils as well as phosphate based functional fluids.
The present invention can provide thiobisphenol phosphorus acid esters having oligomeric and polymeric character which can be linear or crosslinked. The polymer compounds of the present invention generally range from viscous liquids through gummy rubber-like solids to brittle rosin-like materials.
The present invention also provides a commercially feasible method of incorporating the stable phosphate and phosphonate structure into a polymer chain.
Prior to the present invention, compounds containing two phosphorus acid esters linked by a sulfur atom have been prepared. The preparation of O,O,O',O'-tetramethyl-O,O'-thiobis (2-chloro-p-phenylene)phosphonothioate has been accomplished by a complex reaction procedure. The procedure requires the preparation of a sulfur-linked bis-phenol and then the reaction of the bis-phenol and the O,O-dialkyl phosphoryl halide (Lovell et al., U.S. Pat. No. 3,390,209, issued June 25, 1968). In addition, prior to the present invention, incorporation of a phosphorus moiety into a polymer chain generally involved a complex reaction and produced a material with a low phosphorus content (Caldwell et al., U.S. Pat. No. 3,378,523, issued Apr. 16, 1968).